Individual semiconductor devices with mesa structures are typically fabricated from a starting substrate by doping the front and back sides of the substrate with impurities of opposite conductivity types using diffusion techniques and subsequently, providing each of the diffusion layers with a respective metal layer. In the prior art, such processing steps are followed by the application of a photoresist layer to each of the metal layers and the formation of an etch mask from the photoresist layers on each side of the substrate using photolithography. This is accomplished by employing a dual exposure system to expose the front and back sides of the wafer to develop the photoresist layers. After developing and patterning the photoresist layers, the exposed regions of the metal layers on both sides of the substrate are etched. Next, silicon etching is performed on both sides of the substrate to simultaneously form a mesa structure and uncover the pn junction. Finally, the photoresist layers on each side of the substrate is removed and the chips are separated.
The photolithographic process requires considerable expenditure for clean rooms, for chemicals, and particularly for the specific, costly dual exposure system. The removal of the photoresist layers causes waste-disposal and cost problems. The photoresist on the metallic contact areas can cause organic residual material to be present on the metal layers and also in the metal pores, so that during attachment of the chips by soldering, problems may arise due to poor solderability.
Accordingly, it is an object of the present invention to provide a process and an auxiliary device for fabricating individual semiconductor devices having a mesa structure, the process being substantially simpler and, in particular, permitting a considerable reduction of the hitherto required expenditure, this also applying to the auxiliary device.